Yes, Frederick Douglass's autobiography is definitely a primary source, regardless of when the actual book you have was published. A primary source is simply one created by a person with first-hand knowledge of the events and times described and which was created at or near the time in question.

Of course, Douglass had first-hand knowledge of his own life. As for the time element, his autobiography was, of course, not written during his childhood or his days as a slave. However, it was still close enough in time to those events for it to qualify.

The date of publication is not relevant to whether something is a primary source. What matters is who wrote it and when.